Hydraulic conductivity of the matric porosity of an unsaturated vertisol: a field and laboratory comparison

Abstract

In many swelling clay soils several types of porosity can be defined: matric, structural and crack porosities. Measuring the hydraulic conductivity associated with the matric porosity is of major interest because soil movements are governed by matric water flows. Our purpose was to determine the matric conductivity of a vertisol from Guadeloupe (French West Indies) under laboratory and field conditions. We used an Eulerian flow description to measure the conductivity of natural vertisol clods in the laboratory with a drying method. In order to take into account soil movements in every direction, we introduced a tensorial analysis of soil deformations and hydraulic conductivity. The instantaneous profile method was used in the field under wetting conditions. Using soil layer thickness transducers we described water flows in a material coordinate system that can deal with volumetric soil deformations. For wet soil the ratio between the hydraulic conductivity measured in the field and that measured at the laboratory was around 10. However, because the spatial variation of the water content was large, no final conclusion could be drawn to explain this discrepancy. We showed that the gradient of the overburden potential was smaller than that of the matric potential in the field experiment.